Field
Embodiments described herein generally relate to a radar transmitter, including a radar transmitter on a chip, a method of calibrating such a radar transmitter and an on-chip power sensor for use in the radar transmitter.
Related Art
U.S. Pat. No. 6,292,140 describes an antenna which is used for the manufacture of bolometer integrated on a silicon chip. The bolometer comprises an opening in the silicon chip, the opening is spanned by two separate thermally isolated structures. A thin-film antenna comprising two parts, is located on the structures with one antenna part on each structure. Radiation received in the larger of the two antenna parts is coupled electromagnetically into the smaller part where it caused a current to flow. A thin-film thermometer measures the temperatures rise of the smaller antenna part, due to the dissipated heat. The bolometer achieves improved performance in comparison to previous bolometer designs because the variation is dissipated in a part of the antenna only and the bolometer is free from impedance-matching constrains of other designs.
US-Patent Application 2011/0174978 A1 describes a thermal infrared sensor provided in a housing with optics and a chip with thermal elements on a membrane. The membrane spans a frame-shaped support body that is a good heat conductor, and the support body has vertical or approximately vertical balls. The object is to provide a thermal pile infrared sensor in monolithic silicium micro-machining technology, wherein the infrared sensor has a high thermal resolution capacity with a small chip size, a high degree of filling and high response rate. The thermal part sensor structure consists of a few long thermal elements per sensor cell. The thermal elements being arranged on connecting webs that connect together hot contacts on an absorber layer to cold contacts of the thermal elements. A membrane is suspended by one or more connecting webs and has, on both sides of the long thermal elements, narrow slits that separate the connecting webs from both the control region and also the support body.
U.S. Pat. No. 4,008,610 describes a self-balancing D.C.-substitution R.F. power measuring system with first and second high gained differential operational amplifiers, a bolometer element, and a reference resistor element. The amplifiers and the two elements are connected in a current loop with one of the elements connected between the output terminals from the differential amplifiers and the other of the elements connected between center points of isolated dual power supplies associated with each of the amplifiers. Current flows out of one amplifier and into the other. The current is driven to a value which maintains the potential between the input terminus of the first amplifier essential equal to zero and a potential between the input terminals of the second amplifier essentially equal to zero. Thus, the current drives the value of the bolometer elements to a resistance which is equal to the resistance of the reference element.
U.S. Pat. No. 7,548,053 B2 describes a wide-band antenna coupled spectrometer using CMOS transistors. To create a broad band spectrometer, a plurality of individual antenna based bolometers are fabricated on the surface of a single spectrometric chip, each bolometer having an individual antenna which is sized differently from all others, thus being responsive to a generally unique frequency of radiation. Each antenna is coupled to a related transistor, which his easily formed using CMOS technology. The antennas are connected to opposite sides of a transistor gate, thus creating a termination resistor for the particular antenna. Multiple outputs from the various antennas are then coupled, thus providing responsiveness to electromagnetic radiation of a very broad spectrum.
FIG. 1A shows a conventional method of calibrating a millimeter-wave transmitter. On the left-hand side, a transmitting path terminating at an antenna element TX is displayed. The transmit path receives the radio frequency (RF) input from the left, while a directional coupler singles-out a portion of the RF in-power which is directed to a diode. The diode is a rather coarse device for measuring a transmit power. In particular for pulsating RF power a diode typically only responds to maximum amplitudes within such a signal. Hence, the diode will not provide a reliable measure for an average transmit power directed towards the diode. The diode will produce a voltage depending on the maximum amplitude of RF power reaching the diode. A similar millimeter-wave transmitter is illustrated in FIG. 1B. In this example, the directional coupler is connected to two sensitive power detectors (e.g., diodes), one configured for the forward (transmitted) signal and another for the reverse (reflected) signal. Typically the diode (or diodes in FIG. 1B) has a characteristic as displayed in the graph on the right side of FIG. 1A. The voltage Vs across the diode varies with the actual transmit-power TX according to the characteristic shown.
In order to reliably measure the (peak) power reaching the diode, it is typically necessary to measure the transmit-power TX directly and use the voltage Vs to correlate the voltage measured across the diode to the transmit-power actually transmitted at the antenna element terminating the transmit path. When implementing such a calibration of the RF output power in the transmit direction, one may determine the peak RF power delivered to the antenna element by evaluating the voltage Vs of the diode.
A drawback of such a calibrating scheme is that it is rather complex. For example, a signal around 77 GHz needs to be measured with expensive and fragile RF equipment such as probes, wave-guides, power meters, potentially comprising frequency extenders, and the like.
A setup of such a calibration scheme further requires knowledge about RF technology and is rather time consuming. It is further to be understood, that there is no means of recalibrating the diode shown in FIG. 1A or detectors (diodes) shown in FIG. 1B, once the system with the antenna elements is already being used. This is due to the fact, that in the application the actual transmit path is connected to an antenna. For recalibration of the diode-based sensor, the antenna has to be replaced by an RF power meter which is difficult if not impossible for most applications.
The exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings.